[Stereotactic convergent-beam irradiation: its current prospects based on clinical results]

"Radiosurgery" is the term for a special concept in radiotherapy. It describes a percutaneous, stereotactically guided irradiation delivering a single high dose with collimated narrow beams. The precise stereotactic localization of the target point and a steep dose gradient outside the target volume allow the administration of high doses to a lesion without damage to adjacent normal tissue. Risk of necrosis, due to a dose volume relationship represents the limits of radiosurgery. Units for radiosurgery were designed at Stockholm using multiple external cobalt-60-gamma sources, at Boston operating with protons of a cyclotron, at Berkeley operating with helium ions accelerated by a synchrocyclotron. An attractive alternative to these complicated and expensive facilities is the use of a modified linear accelerator. At the German Cancer Research Center in Heidelberg such a system was developed and has been available for the treatment of patients since 1984. Though, data of over 100,000 patients with vascular malformations and cancer disease are available worldwide, the indication for this therapy is validated only for a minority of entities. In cases of inoperable arteriovenous malformations favourable results in achieving obliteration range between 60% and 100% were obtained. Median survival for solitary brain metastases with controlled, extracerebral tumor diseases were between nine and twelve months. Up to now, advantages of stereotactic irradiation for benign tumor masses could not be proven. Therefore, randomized trials should be initiated in this field, considering decisive improvements in local tumor control with techniques of microsurgery and fractionated, postoperative radiotherapy during the last few years.